Curing of adhesives, sealants, and coatings based on conjugated diolefins and, optionally, vinyl aromatics has increased the range of service properties for such compositions. Chemical or radiation curing of reactive conjugated diene polymers to make such crosslinked compositions is known. This curing causes covalent crosslinking of the polymerized conjugated dienes which is evidenced by a high gel content of the crosslinked polymer. Before crosslinking, the polymers are melt and solution processable but after crosslinking, the gel cannot be processed as melts or in solution. Crosslinking therefore enhances solvent resistance and improves elevated temperature shear properties, toughness and cohesion. Compositions can therefore be applied to a substrate in a melt or from solution and then crosslinked to form a superior adhesive, coating or sealant.
The presence of styrene blocks in the reactive conjugated diene polymers can result in a phase separated reactive block copolymer which can cure to form a phase separated adhesive, sealant, or coating. However, the styrene containing polymers are more difficult to process since the styrene blocks promote physical crosslinking of the reactive polymers prior to curing.
Curable adhesives, sealants and coatings which are based on epoxidized polymers are described in U.S. Pat. No. 5,229,464, issued Jul. 20, 1993, (T4797X) which is incorporated by reference herein. The epoxidized polymers may be blended with other reactive polymers as disclosed in the '464 patent to provide a balance of desired properties.
It is an object of the present invention to provide improved adhesive, sealant, and coating compositions which are easily processable in the melt or at high solids content before crosslinking but have a high gel content after crosslinking. Further, it is an object of this invention to provide an adhesive, coating or sealant composition which is based on this improved crosslinked block copolymer composition that achieves a unique balance of tack and strength properties.